Prolonged space flight-induced alterations in the structure and function of human skeletal muscle fibres (original) (raw)
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Exercise in space: Human skeletal muscle after 6 months aboard the international space station
The aim of this investigation was to document the exercise program used by crewmembers (n ϭ 9; 45 Ϯ 2 yr) while aboard the International Space Station (ISS) for 6 mo and examine its effectiveness for preserving calf muscle characteristics. Before and after spaceflight, we assessed calf muscle volume (MRI), static and dynamic calf muscle performance, and muscle fiber types (gastrocnemius and soleus). While on the ISS, crewmembers had access to a running treadmill, cycle ergometer, and resistance exercise device. The exercise regimen varied among the crewmembers with aerobic exercise performed ϳ5 h/wk at a moderate intensity and resistance exercise performed 3-6 days/wk incorporating multiple lower leg exercises. Calf muscle volume decreased (P Ͻ 0.05) 13 Ϯ 2% with greater (P Ͻ 0.05) atrophy of the soleus (Ϫ15 Ϯ 2%) compared with the gastrocnemius (Ϫ10 Ϯ 2%). Peak power was 32% lower (P Ͻ 0.05) after spaceflight. Force-velocity characteristics were reduced (P Ͻ 0.05) Ϫ20 to Ϫ29% across the velocity spectrum. There was a 12-17% shift in myosin heavy chain (MHC) phenotype of the gastrocnemius and soleus with a decrease (P Ͻ 0.05) in MHC I fibers and a redistribution among the faster phenotypes. These data show a reduction in calf muscle mass and performance along with a slow-tofast fiber type transition in the gastrocnemius and soleus muscles, which are all qualities associated with unloading in humans. Future long-duration space missions should modify the current ISS exercise prescription and/or hardware to better preserve human skeletal muscle mass and function, thereby reducing the risk imposed to crewmembers.
Sarcolab pilot study into skeletal muscle’s adaptation to long-term spaceflight
npj Microgravity, 2018
Spaceflight causes muscle wasting. The Sarcolab pilot study investigated two astronauts with regards to plantar flexor muscle size, architecture, and function, and to the underlying molecular adaptations in order to further the understanding of muscular responses to spaceflight and exercise countermeasures. Two crew members (A and B) spent 6 months in space. Crew member A trained less vigorously than B. Postflight, A showed substantial decrements in plantar flexor volume, muscle architecture, in strength and in fiber contractility, which was strongly mitigated in B. The difference between these crew members closely reflected FAK-Y397 abundance, a molecular marker of muscle’s loading history. Moreover, crew member A showed downregulation of contractile proteins and enzymes of anaerobic metabolism, as well as of systemic markers of energy and protein metabolism. However, both crew members exhibited decrements in muscular aerobic metabolism and phosphate high energy transfer. We conclu...
Effects of long-term spaceflight on mechanical properties of muscles in humans
Journal of Applied Physiology, 2001
The effects of long-term spaceflight (90–180 days) on the contractile and elastic characteristics of the human plantarflexor muscles were studied in 14 cosmonauts before and 2–3 days after landing. Despite countermeasures practiced aboard, spaceflight was found to induce a decrease in maximal isometric torque (17%), whereas an index of maximal shortening velocity was found to increase (31%). In addition, maximal muscle activation evaluated during isokinetic tests decreased by 39%. Changes in musculotendinous stiffness and whole joint stiffness were characterized by means of quick-release movements and sinusoidal perturbations. Musculotendinous stiffness was found to be increased by 25%. Whole joint stiffness decreased under passive conditions (21%), whereas whole joint stiffness under active conditions remained unchanged after spaceflight (−1%). This invariance suggests an adaptive mechanism to counterbalance the decrease in stiffness of passive structures by an increased active sti...
Effect of short-duration spaceflight on thigh and leg muscle volume
Medicine & Science in Sports & Exercise, 2000
Human skeletal muscle probably atrophies as a result of spaceflight, but few studies have examined this issue. Thus, little is known about the influence of microgravity upon human skeletal muscle, nor is it possible to assess the validity of ground based models of spaceflight. This study tested the hypothesis that the magnitude of spaceflight induced muscle atrophy would be a function of flight duration and greater than that of bed rest. Methods: Three astronauts flew 9, 15, and 16 d in space. Volume of the knee extensor (quadriceps femoris), knee flexor (hamstrings, sartorius, and gracilis), and plantar flexor (triceps surae) muscle groups was measured using magnetic resonance imaging before and after spaceflight and during recovery. The volume of each muscle group in each image was determined by multiplying cross-sectional area by slice thickness. These values were subsequently summed to calculate muscle volume. Results: Volume changes in the knee extensor, knee flexor, and plantar flexor muscle groups ranged from Ϫ15.4 to Ϫ5.5, Ϫ14.1 to Ϫ5.6, and Ϫ8.8 to Ϫ15.9%, respectively. Muscle volume decreases normalized by flight duration ranged from 0.62 to 1.04%⅐d Ϫ1. These relative changes appeared to be greater than those that we have reported previously for bed rest (Akima et al., J. Gravitat. Physiol. 4:15-22, 1997). Conclusions: These results suggest that atrophy as a result of at least 2 wk of spaceflight varied among individuals and muscle groups and that the degree of atrophy appeared to be greater than that induced by 20 d of bed rest.
Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres
The Journal of Physiology, 1999
The countermeasures employed during spaceflights have not been completely successful in preventing reductions in muscle mass and alterations in neuromuscular performance (Grigoryeva & Kozlovskaya, 1987; Edgerton et al. 1995). In a variety of animal models, changes in muscle recruitment patterns (Roy et al. 1996), muscle fibre type composition (Caiozzo et al. 1996), cellular processes of excitation-contraction coupling (Stevens & Mounier, 1992) and crossbridge mechanisms of contraction (Reiser et al. 1987; Gardetto et al. 1989; McDonald & Fitts, 1993; Widrick et al. 1996) occur in the absence of weight-bearing activity. A better understanding of how humans respond to spaceflight is a requirement for the development of more effective countermeasures. This knowledge will most probably be attained by utilizing experimental approaches capable of isolating specific aspects of the human neuromuscular system for study.
Running Title: Exercise and skeletal muscle with spaceflight Address for Correspondence
2015
The aim of this investigation was to document the exercise program used by crewmembers (n=9; 45±2 y) while aboard the International Space Station (ISS) for 6 months and examine its effectiveness for preserving calf muscle characteristics. Before and after spaceflight, we assessed calf muscle volume (MRI), static and dynamic calf muscle performance, and muscle fiber types (gastrocnemius and soleus). While on the ISS, crewmembers had access to a running treadmill, cycle ergometer and resistance exercise device. The exercise regimen varied among the crewmembers with aerobic exercise performed ~5 hr/wk at a moderate intensity and resistance exercise performed 3-6 d/wk incorporating multiple lower leg exercises. Calf muscle volume decreased (P<0.05) 13±2 % with greater (P<0.05) atrophy of the soleus (-15±2%) compared to the gastrocnemius (-10±2%). Peak power was 32 % lower (P<0.05) after spaceflight. Force-velocity characteristics were reduced (P<0.05)-20 to-29 % across the v...
Medicine & Science in Sports & Exercise
Exercise countermeasures currently administered on the International Space Station are time-consuming and use large/expensive equipment. It has been established that aerobic exercise can maintain oxidative capacity of muscle fibers, while resistance exercise can help preserve muscle mass in Astronauts and individuals in bed rest. Recently, concurrent exercise (CE) training, combining both modes, has been implemented to save time and yield similar benefits. Cotter et al. (2015) determined that CE is effective at mitigating deconditioning during simulated microgravity (unilateral lower limb suspension, ULLS) but there were differences in fiber-type responses (i.e., fast-twitch vs slow-twitch). This thesis provides additional analyses of muscle samples used in Cotter et al. (2015), investigating soleus muscle (mostly slow-twitch) myonuclei (which help to maintain cell size and function). Modulations in fiber size and myonuclear domain (MND; the area each myonuclei controls) may provide mechanisms for preventing unloading decrements. Our aim was to determine 1) if simulated microgravity affects soleus muscle fiber size and MND size and 2) if CE training mitigates these changes. Previously, 19 subjects were separated into two groups, 10-day ULLS and 10day ULLS + CE. Muscle biopsies were taken pre-and post-intervention, which were isolated into individual fibers (muscle cells), stained for myonuclei, imaged, and analyzed EFFECTS OF CONCURRENT EXERCISE DURING SIMULATED MICROGRAVITY ON SOLEUS MUSCLE FIBER MYONUCLEAR CONTENT for fiber size and MND size. 2x2 ANOVAs determined potential differences in fiber size and MND size between groups, before and after ULLS. Neither group showed significant differences in fiber size or MND size after 10 days of ULLS. These findings suggest that, while 10 days of ULLS may cause a decline in muscle function (as seen in Cotter et al., 2015), it may not be long enough to significantly affect soleus muscle fiber size or MND size. However, inter-individual responses varied from subject to subject, suggesting that some people may be responders (or non-responders) to ULLS and ULLS+CE. This suggests a need for additional analyses among individual participant to help develop "personalized" exercise countermeasures for those undergoing significant periods of unloading (e.g., people in bed rest or Astronauts).
Comparison of a space shuttle flight (STS-78) and bed rest on human muscle function
Journal of Applied Physiology, 2001
The purpose of this investigation was to assess muscle fiber size, composition, and in vivo contractile characteristics of the calf muscle of four male crew members during a 17-day spaceflight (SF; Life and Microgravity Sciences Spacelab Shuttle Transport System-78 mission) and eight men during a 17-day bed rest (BR). The protocols and timelines of these two investigations were identical, therefore allowing for direct comparisons between SF and the BR. The subjects' age, height, and weight were 43 ± 2 yr, 183 ± 4 cm, and 86 ± 3 kg for SF and 43 ± 2 yr, 182 ± 3 cm, and 82 ± 4 kg for BR, respectively. Calf muscle strength was examined before SF and BR; on days 2, 8, and 12 during SF and BR; and on days 2 and 8 of recovery. Muscle biopsies were obtained before and within 3 h after SF (gastrocnemius and soleus) and BR (soleus) before reloading. Maximal isometric calf strength and the force-velocity characteristics were unchanged with SF or BR. Additionally, neither SF nor BR had any...
Muscle changes with eccentric exercise: implications on Earth and in space
Advances in myochemistry, 1989
In this paper, we review recent investigations of fluid pressure, morphology, and enzyme activities of skeletal muscle exercised eccentrically or concentrically i n normal human subjects. Intramuscular pressures were measured before, during, and after submaximal exercise and correlated with subjective muscle soreness, fiber size, water content, and blood indices of muscle enzymes. High-intensity eccentric exercise is characterized by postexercise pain, elevated intramuscular pressures, and swelling of both type 1 and 2 fibers as compared to concentric exercise. Thus, long periods of unaccustomed, high-level eccentric contraction may cause muscle injury, fiber swelling, fluid accumulation, elevated intramuscular pressure, and delayed muscle soreness. Training regimens of progressively increasing eccentric exercise, however, cause less soreness and are extremely efficacious in increasing muscle mass and strength. It is proposed that on Earth, postural muscles are uniquely adapted to low levels of prolonged eccentric contraction that are absent during weightlessness. The almost complete absence of eccentric exercise in space may be an important contributor to muscle atrophy and therefore equipment should be designed to integrate eccentric contractions into exercise protocols for long-term spaceflight.